Process for producing polysilicon film

ABSTRACT

The present invention provides a process for producing a polycrystal silicon film which comprises a step of forming a polycrystal silicon film by light irradiation of a silicon film set on a substrate, and a step of selecting substrate samples having an average grain size in a plane of the sample of 500 nm or more. According to the present invention, stable production of a high-performance poly-silicon TFT liquid crystal display becomes possible.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 10/059,203filed Jan. 31, 2002 now U.S. Pat. No. 6,806,099.

BACKGROUND OF THE INVENTION

The present invention relates to a process for producing a poly-silicon(hereinafter abbreviated as poly-Si) film for liquid crystals andsemiconductor devices, and a method for inspecting the poly-siliconfilm.

The reason why a poly-silicon film is superior to an amorphous silicon(a-Si) film as the active layer of a thin film transistor (TFT) used asa driver element in a liquid crystal display is as follows: in the caseof the poly-silicon film, since the mobility of a carrier (electrons inn channel or holes in p channel) is high, the cell size can be reduced,so that the precision and minuteness of the liquid crystal display canbe enhanced. In addition, the formation of a conventional poly-Si TFTrequires a high-temperature process at 1,000° C. or higher. On the otherhand, a TFT having a high carrier mobility can be formed in alow-temperature process permitting employment of an inexpensive glasssubstrate, when there is adopted a low-temperature poly-siliconformation technique in which annealing of only a silicon layer with alaser does not make the temperature of the substrate high.

In this laser annealing, as shown in FIG. 13, an a-Si film formed on aglass substrate is scanned while being irradiated with light absorbablethereby, to make the whole a-Si film into a polycrystal, whereby apoly-Si film is obtained. As shown in FIG. 14, the poly-Si grain sizevaries with the surface density of irradiation energy (fluence) of alaser, so that the stability of the laser reflects on the grain sizedistribution of the poly-Si. The carrier mobility of the poly-Si filmincreases with an increase of the grain size. In order to attain highTFT characteristics with in-plane uniformity, it is necessary to makethe grain size distribution uniform and maintain a large grain size. Toattain the large grain size, employment of a fluence in the D regionshown in FIG. 14 is sufficient. However, if the fluence shifts upwardowing to the instability of the laser, or the like, the fluence enters aregion shown as the E region in FIG. 14, i.e., a region where thepoly-Si film contains micro crystals with a grain size of 200 nm orless. In this case, the carrier mobility is decreased, resulting in afaulty device. The grain size varies not only with the laser fluence butalso with the nonuniformity of thickness of the a-Si film before thelaser annealing. Therefore, in order to form the poly-Si film so thatits grain size may always be in a definite range, the laser instabilityand the thickness change of the substrate have to be kept slight. Forthis purpose, control of the grain size is necessary. Accordingly, itbecomes important to control the poly-Si grain size to keep it constant,by checking the poly-Si grain size and feeding back the check result tothe laser annealing conditions.

As a method for the control, measuring the grain size itself of thepoly-Si is the most reliable. The grain size has been measured byincorporating a sample for the check into an initial or intermediateproduction lot, or by randomly sampling a product and directly observingthe grain size of a poly-Si film formed in a production process, by anelectron microscope or a scanning tunnel microscope. As other priorarts, there are the following methods. Japanese Patent. Kokai No.10-214869 discloses a method in which a poly-silicon film is evaluatedon the basis of its transmittance. According to this method, the grainsize cannot be estimated, though insufficient crystallization due to theinsufficient fluence of laser beams can be monitored on the basis of theratio between a-Si and a poly-Si by utilizing the difference inabsorption coefficient between a-Si and the poly-Si. Japanese PatentKokai No. 11-274078 discloses a method in which a poly-silicon film isevaluated on the basis of its surface gloss (reflectance). In thismethod, the change of the gloss with the poly-Si grain size is utilizedand the gloss is considered to be minimal at an optimum poly-Si grainsize. This optimum poly-Si grain size corresponds to a grain size atwhich the reflectance becomes minimal, namely, the surface roughnessbecomes maximal.

SUMMARY OF THE INVENTION

The pressure resistance of the gate insulating film of a device becomesinsufficient if the surface roughness of the film is high. Thus, a grainsize detected by the utilization of conditions under which the surfaceroughness becomes maximal is used in a method in which there is detecteda region where the risk of insufficient pressure resistance due to aremarkable surface unevenness is the highest. If this region isemployed, a process for reducing the surface roughness is required,resulting in a complicated production process. Thus, a device productionprocess dependent on the above-mentioned prior art substrate examinationmethods requires a special process for reducing the surface roughness,and its adoption is limited to that at a grain size (about 300 nm) inthe B region shown in FIG. 14. However, a poly-Si film having a highercarrier mobility has to be formed in order to produce a liquid crystalwhich consumes less electricity and has higher precision and minuteness.To form such a poli-Si film, it is sufficient that there is employed theD region shown in FIG. 14, i.e., a region in which the grain sizebecomes maximal. For this purpose, it is necessary to estimate the grainsize, independent of the surface roughness. As a method for determiningthe D region, the above prior arts are not suitable and examination byelectron-microscopic observation is not suitable for determination onthe site of a mass production line because it requires human labor and along time for obtaining a measurement result. Accordingly, it isdifficult to produce stably a poly-Si substrate having a low surfaceroughness and a grain size of more than 300 nm. The present inventionwas made in view of the above problems, and makes it possible todetermine a region where the surface roughness is low and the grain sizeof a poly-Si is maximal, by a simple method. Thus, the present inventionis intended to provide a process for producing a poly-Si film having alow surface roughness and a high carrier mobility, without productnonuniformity or in high yield.

For the achievement of the above object, the present invention providesa process for producing a poly-Si film which comprises a step of forminga poly-Si film by annealing a silicon film set on a substrate, by lightirradiation, a step of measuring a light diffraction pattern of thepoly-Si film, and a step of selecting the poly-Si film on the basis ofthe light diffraction pattern.

The aforesaid silicon film is composed of an a-Si film and is convertedto a poly-Si film by annealing by laser beam irradiation. The grain sizeof the poly-Si film is estimated by measuring the angular distributionof scattered light intensities, and the quality of the poly-Si film isjudged by knowing whether its grain size is in the range of the upperlimit of the average grain size to the lower limit which range isdefined by the relationship between the field-effect mobility and thegrain size.

As shown in FIG. 1, a light source 2 used for the above-mentionedpoly-silicon size measurement with angle dependency of scattered lightintensity is a laser having an output wavelength of 540 nm or less andemits laser beams perpendicularly to a substrate 1 having theabove-mentioned poly-Si film formed thereon. A plurality of lightdetector units 7 are located at their respective angles in a range ofabout 5° to about 45° in order to measure the angular distribution ofthe intensities of scattered lights from the irradiation region. Asshown in FIG. 7, the relationship between the poly-Si grain size and thebreadth of angular distribution of scattered light intensities in thelight diffraction pattern of the poly-Si film is explainable in terms ofa relation based on Fourier transformation which is such that ingeneral, the breadth of angular distribution of the intensities ofscattered light from particles decreases with an increase of theparticle size. FIG. 7 shows both the case of single particles notinterfering with one another and the case of densely aggregatedparticles interfering with one another. In the latter case, thedistribution is such that the scattered light intensity decays at ascattering angle close to zero. In either case, when distribution A witha larger breadth of angular distribution and distribution B with asmaller breadth of angular distribution are compared for the grain size,the grain size in the case of distribution B can be judged to be largerthan in the case of distribution A. According to this principle, thegrain size is measured without destruction.

In the above process for producing a poly-Si film, there is measured thebreadth of angular distribution of scattered light intensities in alight diffraction pattern of a poly-Si formed as a thin film byirradiating a-Si with exciter laser beams, in the production procedureof a poly-Si. From the measurement result, the grain size of the poly-Siis estimated. On the basis of the estimation result, the fluence ofanneal laser beams is set. When the fluence of anneal laser beams is toolow, the grain size does not become sufficiently large. Therefore, thelower limit of the fluence is fixed.

On the other hand, in a region where micro crystals are formed as shownin FIG. 17 because of too high a fluence, the average grain size isdecreased and a linear pattern appears in a light diffraction pattern asshown in FIG. 18. Micro-crystal streak lines are detected by detectingthe linear pattern. The upper limit of the fluence of anneal laser beamsis fixed so that the micro crystal streak lines may not appear. Thelower limit and upper limit of the laser fluence are fixed as follow inthe range of control of the average grain size.

The range of control of the average grain size (the upper limit andlower limit of the average grain size) is determined from a desirablefield effect mobility and the range of variation of in-planedistribution of field effect mobility by utilizing the relationshipbetween the average grain size and the field effect mobility shown inFIG. 15.

In order to determine the laser annealing conditions before theproduction, annealing is conducted under laser fluence conditionsstepwise varied in a substrate, after which the average grain size isestimated from the breadth of angular distribution in a lightdiffraction pattern of the resulting poly-silicon film, and the laserannealing conditions are determined so that the average grain size maybe in the range of control. In an actual process, the reduction of theproduct nonuniformity and the improvement of the yield are carried outby estimating the in-plane distribution of the grain size of a poly-Sifilm after laser annealing, judging the quality of the substrate sampleobtained by the laser annealing, according to the above-mentionedcriterion, and sending the sample to a subsequent step only when it isjudged good. In this case, a total inspection need not always be carriedout, and either a sampling inspection or a total inspection may bechosen depending on the range of variation of the average grain size ofeach substrate sample in one and the same lot. That is, when the rangeof variation of the average grain size of each substrate sample in oneand the same lot is in a range of ±20%, inspection of at least onesubstrate sample in one and the same lot is sufficient. In aconventional sampling inspection, three samples, i.e., the first sample,an intermediate sample and the last sample in each lot are inspected.When the range of in-plane variation of the average grain size is in arange of ±20% for all of the three samples, the whole lot is consideredas a good lot. However, if the range of variation of the average grainsize of even only one of the three substrate samples is outside therange of ±20%, the sampling inspection for the lot is switched over to atotal inspection.

Thus, substrate samples are screened by the total inspection or thesampling inspection. According to the data shown in FIG. 15, bycontrolling the grain size so that the average grain size may be 500 nmor more and that the range of variation of the average grain size in thein-plane distribution of average grain size values may be in a range of±20%, there is formed a poly-silicon film having a field effect mobilitynot less than a set value 200 cm²/VS and an in-plane variation of fieldeffect mobility in a range of ±10%.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an example of structure for explaining amethod for estimating the grain size of a poly-silicon according to thepresent invention.

FIG. 2A and FIG. 2B are diagrams showing a structure of equipment (amulti-beam type) for grain size measurement and check based on a lightdiffraction pattern.

FIG. 3 is a diagram showing another example of structure for explaininga method for estimating the grain size of a poly-silicon according tothe present invention.

FIG. 4A and FIG. 4B are diagrams showing another structure of equipment(a multi-beam type) for grain size measurement and check based on alight diffraction pattern.

FIG. 5 is a diagram showing still another example of structure forexplaining a method for estimating the grain size of a poly-siliconaccording to the present invention.

FIG. 6 is a diagram showing the structure of a laser annealing equipmentincorporated with a grain-size-measuring function based on a lightdiffraction pattern.

FIG. 7A and FIG. 7B are diagrams for explaining a principle ofpoly-silicon grain size estimation according to the present invention.

FIG. 8 shows a table summarizing experimental data obtained byinvestigating the relationships among a light diffraction pattern ofeach poly-silicon, its grain size and its roughness.

FIG. 9 is a graph obtained by investigating the laser fluence dependenceof the breadth of angular distribution of scattered light intensities ina light diffraction pattern.

FIG. 10A, FIG. 10B and FIG. 10C are diagrams showing poly-silicon grainboundaries observed in one and the same sample by SEM.

FIG. 11 is a diagram showing the array of detector units for measuring alight diffraction pattern.

FIG. 12 is a diagram showing an optical detection system in the casewhere a detector for measuring a light diffraction pattern is of atwo-dimensional detection type.

FIG. 13 is a diagram showing a polycrystal silicon formation processemploying laser annealing.

FIG. 14 is a graph showing the relationships among laser fluence,poly-Si grain size and surface roughness.

FIG. 15 is a graph showing the relationship between poly-Si grain sizeand carrier mobility.

FIG. 16 is a chart showing a method for feedback to a laser annealingprocess on the basis of information on a grain size check.

FIG. 17 shows the appearance of micro crystal steak lines in the case ofa high-fluence region.

FIG. 18 is a schematic view of a light diffraction pattern in the casewhere micro crystal streak lines are present.

FIG. 19 shows an example of representation of an inspection result.

DESCRIPTION OF REFERENCE NUMERALS

1 - - - substrate sample obtained by forming a poly-silicon film on aglass substrate, 2 - - - source of irradiation laser beams, 3 - - -irradiation laser beam, 4 - - - half mirror, 5 - - - mirror, 6 - - -irradiation light intensity monitor, 7 - - - detection surface for lightdiffraction pattern, 8 - - - substrate-supporting pedestal, 9 - - -frame for fixing optical irradiation system and optical detectionsystem, 10 - - - scattered light, 11 - - - vacuum chuck hole forsubstrate fixation, 11-1 - - - detector unit, 11-2 - - - aperture,12-1 - - - two-dimension detector, 12-2 - - - lens, 12-3 - - - poly-Sifilm on glass, 13-1 - - - line beam pulse excimer laser, 13-2 mirror,13-3 - - - poly-Si film, 17-1 - - - direction of long axis ofirradiation beam of anneal laser, 18-1 - - - diffraction pattern fromboundary between micro crystal grain region and fused crystal grainregion, 18-2 - - - ring-shaped light diffraction pattern reflecting meangrain size.

DETAILED DESCRIPTION OF THE INVENTION

As a results of experiments by the present inventor, the following wasfound: when the grain size of the poly-silicon formed is maximal and thepoly-silicon contains no micro crystal, the electric conductivity ishigh and the breadth of angular distribution of the intensities ofscattered light from the thin film formed by excimer laser annealing(ELA) is minimal.

The experimental data are shown in the table in FIG. 8. The dataindicate the angle dependency of the intensity of scattered light fromthe poly-Si film and the laser fluence dependency of SEM observationresults and AFM observation results. As a result of the SEM observation,the following was found: when the fluence is 420 mJ/cm², there isobtained a similarly sized crystal grain region where the grain size isabout 300 nm; according as the fluence is increased, there are obtainedcrystals each formed by fusion of a plurality of grains having a grainsize of about 300 nm; and with the progress of the fusion, the averagegrain size is increased. At a fluence close to 470 mJ/cm², the fusionrate in the poly-Si grain boundaries is maximal, resulting in a maximumaverage grain size. In the case of a poly-silicon having a uniform grainsize, a projection is present at the triple point of boundaries. A fusedcrystal is a crystal formed by fusion of a plurality of uniform grainsand has a shape having projections in grain boundaries owing to thefusion. According to the AFM observation, the maximum height difference(PV), an indication of roughness is 60 nm or more in the case of auniform grain size, and is decreased to less than 60 nm with theprogress of fusion. The root mean square roughness (RMS) is more than 8nm in the case of a uniform grain size, and is decreased to less than 8nm with the progress of fusion. These results agree with therelationship between grain size and roughness shown in FIG. 14.

FIG. 9 is a graph showing the fluence dependency of the reciprocal ofthe breadth of angular distribution in a light diffraction patternmeasured by the use of the measurement system shown in FIG. 1. It can beseen that as shown in FIG. 9, the breadth of angular distributiondecreases (namely, 1/the breadth of angular distribution increases) withan increase of the fluence, and it increases (namely, 1/the breadth ofangular distribution decreases) when the fluence exceeds about 490mJ/cm² or more. FIG. 10 shows the grain boundaries in SEM photographs ofthe same samples as in the case of FIG. 9. A sample obtained at afluence of 420 mJ/cm² has a grain size of about 300 nm which is in asimilarly sized crystal grain region. A sample obtained at a fluence of480 mJ/cm² has an average grain size of 500 nm or more owing to fusion.A sample obtained at a fluence of 510 mJ/cm² shows the presence thereinof micro crystals together with crystals with a large grain size formedby fusion. Therefore, the graph shown in FIG. 9 indicates that thebreadth of angular distribution decreases with an increase of thepoly-Si grain size. In addition, this graph corresponds to the graphshown in FIG. 14 and showing the fluence dependence of the grain size,and indicates that it is possible to detect a D region where theroughness is low and the grain sized is maximal. In the presentinvention, optimum conditions for the laser annealing are determined byutilizing the following fact: a state capable of minimizing the breadthof angular distribution of scattered light intensities is a conditionunder which the grain size becomes maximal and no micro crystal ispresent together with crystals with a large grain size, and hence thestate gives the highest field effect mobility. Furthermore, on the basisof the result of measurement of the grain size, rejects arediscriminated and prevented from flowing into the subsequent step forthe production, or the measurement result is fed back to a set value ofthe fluence for the laser annealing. Thus, a poly-Si film is alwaysproduced under the optimum conditions, whereby the yield is increased.

FIG. 16 illustrates the above steps of procedure schematically.Information obtained by checking the grain size is sent to acentral-control computer and fed therefrom back to the productionprocess as, for example, information on the flow of a substrate samplefor a carrier robot and information on the change of process parametersfor a production equipment. The carrier robot carries the substratesample from a laser annealing equipment to a grain size measurementequipment or from the latter to the former, and the robot and theequipments communicate with one another by means of a network. A poly-Sisubstrate sample produced by the laser annealing equipment is carried tothe grain size measurement equipment by the carrier robot and evaluated.To the central-control computer and the laser annealing equipment, thegrain size measurement equipment gives information on the result ofjudging the quality of each substrate sample according to a definitecriterion and the grain size in-plane distribution of a substrate samplejudged no good. A substrate sample judged good is carried to theproduction equipment used in the subsequent step. The substrate samplejudged no good is returned to the laser annealing equipment for thepurpose of re-annealing. In the grain size measurement equipment, thefollowing is carried out besides the judgment of the quality: for thesubstrate sample judged no good because of its small grain size, theside on which the conversion to micro crystals has took place is judgedto be either a high-fluence side or a low-fluence side, wherebyconditions for the laser re-annealing are determined. As to a method forjudging that micro crystals have been formed on the high-fluence side,this judgment is made when the C region shown in FIG. 14 is present in apart of the grain size in-plane distribution in a definite proportion ormore and a micro crystal grain region is present together therewith. Asto a method for judging that micro crystals have been formed on thelow-fluence side, this judgment is made when the B region shown in FIG.14 is present in a part of the grain size in-plane distribution in adefinite proportion or more and a micro crystal grain region is presenttogether therewith.

A method for determining the laser re-annealing conditions is describedbelow in detail. As to the laser re-annealing conditions for a substratesample whose micro crystals have been judged to be those formed on thehigh-fluence side, the re-annealing is carried out at a fluence lowerthan the initial laser fluence. As to the laser re-annealing conditionsfor a substrate sample whose micro crystals have been judged to be thoseformed on the low-fluence side, the re-annealing is carried out at afluence higher than the initial laser fluence. As a method for there-annealing, there are two methods, i.e., a method of re-annealing anarea where the micro crystals are present, and a method of re-annealingthe whole substrate sample surface. In the case of a substrate sample inwhich micro crystals are present together with grains having grain sizesin the B region and the C region, only an area where the micro crystalsare present is re-annealed, or the idea of re-annealing is given up andthe substrate sample is judged to be one which has to be discarded.Conditions for the re-annealing in this case are as follows. When thegrain size range of grains near the micro crystals is in the B region, afluence higher than the initial fluence is employed. When the grain sizerange of grains near the micro crystals is in the C region, a fluencelower than the initial fluence is employed.

FIG. 15 is a graph obtained by investigating the relationship betweenfield effect mobility measured in a poly-Si TFT and the grain size ofthe poly-Si. A region where the field effect mobility becomes a uniformvalue, i.e., about 250±15 cm²/VS is present near a grain size of 800 nm.The relationship between the field effect mobility and the variation ofthe grain size is determined from the slope of the straight line shownin FIG. 15, to find that the variation of the average grain size has tobe in a range of ±20% in order to keep the variation of the field effectmobility in a range of ±10%. The result of estimating the grain size isfed back to the process so as to control the grain size. By thefeedback, a poly-Si TFT having a field effect mobility in a range of250±15 cm²/VS can be produced. In this case, the in-plane variation ofthe mobility is in a range of ±10%.

A mode for practicing a grain size measuring method is described below.

FIG. 1 is a diagram showing a method for measuring the grain size of apoly-Si according to one embodiment of the present invention. First, asample 1 is prepared by irradiating an a-Si film constituting theuppermost layer of a laminate obtained by laminating at least one thinfilm on a glass substrate by a plasma CVD method, with excimer laserbeams with a wavelength of about 300 nm to convert the a-Si film to apolycrystal. This sample is irradiated with light from a laser beamsource 2 with an output wavelength of 532 nm perpendicularly to thesample surface from the side reverse to the side on which a poly-Si filmhas been formed. The intensities of scattered light from the poly-Sifilm are measured with a plurality of light detector units 7 located attheir respective angles on the side on which the poly-Si film has beenformed. The angle range for the, measurement is a range of 5° to 45°.According to a relation based on Fourier transformation, therelationship between the particle size of a light-scattering substanceand the breadth of angular distribution of scattered light intensitiesis as follows: with an increase of the particle size, the angulardistribution of scattered light intensities becomes that at lowerangles, namely, the breadth of angular distribution of scattered lightintensities is decreased; and with a decrease of the particle size, thebreadth of angular distribution is increased. By utilizing the principledescribed above, the grain size of the poly-Si film is estimated bymeasuring the breadth of angular distribution of scattered lightintensities. The grain size is determined by using a calibration curveshowing the relationship between the grain size and the breadth ofangular distribution which has previously been obtained. As a method formeasuring the breadth of angular distribution, there is a method ofmeasuring the breadth by setting a plurality of detector units at theirrespective angles in one-dimensional array on a diffraction surface asshown in FIG. 11, and a method of measuring a light diffraction patternwith a two-dimension light detector as shown in FIG. 12. In bothmethods, irradiation beams have to be prevented from entering thedetector directly.

FIG. 3 is a diagram showing a method for estimating the grain size of apoly-Si according to another embodiment of the present invention. Thatis, FIG. 13 shows a method comprising irradiating a sample 1 with laserbeams perpendicularly from the side on which the poly-Si film of thesample 1 has been formed, and measuring a diffraction pattern in adirection in which back scattering is detected. FIG. 5 shows a methodfor measuring a light diffraction pattern in the case of obliqueincidence of irradiation light. As an actual production process, aprocess for producing a liquid crystal display by the use of the methodfor estimating the grain size of a poly-Si according to the presentembodiment can be practiced by carrying out an inspection withoutdestruction and contact. Therefore, it is needless to incorporate adummy sample into a production lot as before, and a product samplinginspection or a total inspection can be carried out. For this purpose, alight diffraction pattern has to be measured within 10 minutes per eachsample, and hence-there is adopted a method in which a plurality ofpositions of a substrate sample are subjected at the same time tomeasurement by scanning by using multiple irradiation laser beams formeasurement as shown in FIGS. 2A and 2B. FIGS. 4A and 4B are diagramsshowing the structure of a measurement system using multiple irradiationlaser beams which is obtained by the use of the measurement system shownin FIG. 3. Employment of such a multiple-beam system reduces themeasurement time. A total inspection is carried out by setting theinspection time at a time shorter than the laser annealing process time.In addition, by providing a laser annealing equipment with a functioncorresponding to the above-mentioned grain size estimation method asshown in FIG. 6, the grain size can be estimated without taking asubstrate sample out of the equipment. In this case, there are a methodin which the grain size of an annealed portion is estimatedsimultaneously with scanning of the substrate sample during annealing,and a method in which the grain size is estimated after completion ofthe annealing. As in a method using a separated estimation equipment,the quality of the substrate sample is judged on the basis of theestimation result. When the substrate sample is no good, whetherre-annealing is conducted or not is judged. When re-annealing isconducted, conditions for it are determined. On the basis of theinformation thus obtained, laser re-annealing is carried out.

FIG. 17 shows the shape of micro crystals present together with othercrystals in the case of the E region shown in FIG. 14. That is, anin-plane region where fused crystals with a grain size of 500 nm or moreare present and an in-plane region where micro crystals with a grainsize of 200 nm or less are present are dependent on the shape of an areairradiated with anneal laser beams, and the micro crystal grain regionis formed so that a boundary between the fused crystals and the microcrystals is formed in parallel with the direction of long axis of theanneal laser beam. This is because the anneal laser beam is pulsed lightand its fluence varies at intervals of one pulse. The micro crystalgrain region having streak lines can be detected on the basis of theaverage grain size determined from the breadth of angular distributionin a light diffraction pattern. In addition, the streak lines aredetected as a linear pattern in the light diffraction pattern. FIG. 18schematically shows the light diffraction pattern containing the linearpattern due to the micro crystal streak lines. The linear patternappears at a scattering angle range of approximately 5° to 10° andextends in the direction of short axis of the anneal laser beam. Todetect the linear pattern, it is sufficient that by the use of thedetector shown in the FIG. 11, the light diffraction pattern is measuredin terms of a quantity proportional to the difference between theintensity of a signal from a detector unit set in the 0° direction andthe intensity of a signal from a detector unit set in the 90° direction.

FIG. 19 shows an example of representation of an estimation resultobtained by the present measurement method. That is, FIG. 19 shows thein-plane distribution of the grain size, the in-plane distribution ofmicro crystal appearance regions, and the in-plane distribution offoreign matters. The foreign matters are detected as portions where theintensity of scattered light is locally high.

In the present embodiment, there is described a process for producing apoly-Si film with a grain size in the D region shown in FIG. 14, thoughthere may be adopted a process in which the production is controlled ina grain size region other than the D region. In this case, the lowerlimit and upper limit of an average grain size set as a productioncondition are fixed. When there is a grain size smaller than the lowerlimit, this information is fed back to the process so as to increase thefluence of anneal laser beams. When there is a grain size larger thanthe upper limit, this information is fed back to the process so as toreduce the fluence of anneal laser beams.

It will be further understood by those skilled in the art that theforegoing description has been made on embodiments of the invention andthat various changes and modifications may be made in the inventionwithout departing from the spirit of the invention and scope of theappended claims.

As described above in detail, according to the present invention, thefollowing process for producing a polycrystal silicon film can beprovided: by utilizing the fact that a diffraction pattern of a poly-Sifilm formed varies depending on the average grain size of the film, thegrain size is estimated by measuring the angular distribution ofscattered light intensities with a plurality of light detector units toevaluate an actual product of large substrate sample without contact anddestruction, therefore the product nonuniformity is low and the yield ishigh owing to early removal of rejects. In particular, it becomespossible to control a poly-Si film with an average grain size largerthan 300 nm, a grain size at which the surface roughness becomes maximalowing to a fluence change. Thus, it becomes possible to mass produce aliquid crystal display comprising a poly-Si film having an average grainsize of 500 nm or more and a range of the in-plane variation of theaverage grain size in a range of ±20%.

1. A process for producing a polycrystal silicon film, comprising thesteps of: forming a polycrystal silicon film by light irradiation of asilicon film formed on a substrate sample; measuring grain size of saidpolycrystal silicon film; and adjusting energy of said light irradiationbased on said grain size, wherein the step of measuring grain size ofthe polycrystal silicon film includes irradiating the substrate samplewith light having a wavelength of 540 nm or less, measuring angledependency of scattered light intensity at least in an angle range of 5°to 40° from an axis of transmitted light, and determining the grain sizefrom information thus obtained on angular distribution.
 2. A process forproducing a polycrystal silicon film, comprising the steps of: forming apolycrystal silicon film by light irradiation of a silicon film formedon a substrate sample; measuring grain size of said polycrystal siliconfilm; and adjusting energy of said light irradiation on the basis ofsaid grain size, wherein the step of measuring grain size of thepolycrystal silicon film includes irradiating the substrate sample withlight having a wavelength of 540 nm or less, measuring angle dependencyof scattered light intensity at least in an angle range of 5° to 40°from an axis of reflected light, and determining the grain size frominformation thus obtained on angular distribution.
 3. A process forproducing a polycrystal silicon film, comprising the steps of: forming apolycrystal silicon film by line beam light irradiation of a siliconfilm formed on a substrate; and measuring grain size of said polycrystalsilicon film, wherein, in the step of measuring grain size of saidpolycrystal silicon film, a difference between actual energy density oflight irradiation and an energy density in which the grain size becomesmaximal is measured, and based on the result of measurement, the energydensity of light irradiation is adjusted.
 4. A process according toclaim 3, wherein a substrate sample is judged good if the grain size ofthe sample is not lower than a predetermined lower limit, and asubstrate sample is judged no good if the grain size is lower than thepredetermined lower limit, the process further comprising a step ofcarrying out light re-irradiation of a substrate sample judged no good,and judging whether the re-irradiated sample is good or no good, wherebyonly a substrate sample which has been judged good is supplied to asubsequent step.